what length anode rod for 50 gallon?

Hi all,

I installed a water heater in my home in February, however I have a water softener and it really chews up water heaters. I installed a 50 gallon power vent Rheem/GE water heater and i wanted to know what length magnesium anode rod to replace it with? I've been looking on amazon for it, and I prefer the flexible over straight, because I don't have that much room to work with. Unfortunately, home depot doesn't carry anode rods, special order.

Camco 11612 5/8-Inch OD by 42-Inch Flexible 3 Section Anode Rod

or

Rheem SP8371B R-Tech Resistor Flexible Magnesium Anode Rod with 54-Inch Length and 0.9-Inch Diameter

I'm assuming installation will be a snap, I have a good size 1/2" breaker bar

As long as it's shorter than the depth of the water in the tank, you should be okay.